Plant Care 101: Ingredients your plant needs to thrive — Humidity

Humidity is the amount of water vapor present in the air. Everyone knows the concept of humidity well -- high levels of humidity in the summer cause chaos to those of us that have thick hair (help!), and low levels of humidity in the winter often lead to dry skin. From a plant perspective, humidity influences the amount of water needed and the health of its leaves.

Humid tropical forest

High levels of humidity decrease the amount of water lost by a plant through transpiration (aka the evaporation of water from a plant’s leaves), and low levels of humidity increase the amount of water lost through transpiration. A plant adapted to a humid environment, but stored in a dry environment, potentially like a home, will need extra watering and care to compensate for the high rate of transpiration.

The ideal humidity for most houseplants (excluding cacti and succulents) is between 40% and 60%. Something to look out for is that residences and office spaces can commonly have between 10–20% humidity (!), especially during drier winter months. Chicago during the Spring and Summer often has humidity greater than 40% (higher in the morning, drier in the afternoon). Greenhouses and rainforests typically have humidity greater than 50%.

The good news is that many robust houseplant species are tolerant of drier, low-humidity environments — perfect for the conditions residences and offices. These plants are considered hardy species because they have developed protective coatings on their leaves to prevent excessive transpiration. Succulents and cacti are examples of houseplants with thick and waxy leaves.

Succulents and Cacti are tolerant of low-humidity

Houseplant species without waxy leaves (plants with thin leaves, like ferns or ponytail palms) are adapted to more humid conditions. These species are considered more difficult to care for, because they prefer higher levels of humidity than what is commonly found in homes and offices. For these plants, high rates of transpiration can cause them to have crispy-brown leaf edges and leaf drop. These crispy leaves are clear signs that the plant’s leaves are stressed and are not getting enough humidity. Thus, in temperature controlled environments (winter: heat / summer: air conditioning), it is important to provide extra care to your plants by increasing both the amount of water they receive, and the humidity of the area around the plant.

Ferns and other thin leafed plants prefer higher humidity levels.

As you know from last week’s blog post, the best way to see if your plant is thirsty is to stick your finger an inch deep into the soil. Keeping your plant from getting too thirsty will go a long way in preventing crispy leaf edges.

Clustering plants to increase humidity

To combat crispy leaves and increase the ambient humidity around your houseplants:

  1. Cluster your plants. The jungle is a very humid place mainly because of its high density of plant life. Huddling your plants close together creates a localized jungle right in your home, which will increase your plant’s relative humidity (More incentive to acquire additional plants from us to grow your urban jungle!).
  2. Spritz your plant daily. Although this is a short lived effect, wet leaves will increase the relative humidity around your houseplant for a few hours. Spritzing is good for all plant species except for those with very hairy stems and leaves, which can trap too much moisture and lead to the formation of disease.
  3. Place a humidity tray underneath your houseplant. A humidity tray is created by filling a stylish tray (copper or wood) with medium size pebbles and water. The water in the tray will constantly evaporate, increasing the relative humidity around your houseplant.
  4. Store your plant in a humid room. Rooms such as the bathroom (shower moisture) and kitchen (boiling water, dishes, etc.) typically have the highest levels humidity in a home.

I hope you now understand the importance of humidity for houseplants and the tricks you can do to increase their relative humidity. As always send questions or comments about plant care to